The present invention relates to turbine rotor blades having an airfoil and a tip shroud carried by the airfoil. More particularly, but not by way of limitation, the present invention relates to edge profiles for tip shrouds of turbine rotor blades.
Turbine rotor blades typically comprise an airfoil, a platform, a shank and dovetail. Oftentimes, the airfoil also includes an integrally formed tip shroud mounted at a tip of the airfoil, which is supported by a fillet formed therebetween. Because rotor blades operate at such high rotational velocities and reside in the hot gas path, they are generally subjected to extreme thermal and mechanical loads. In the case of the tip shroud, however, because it is positioned at the outer tip of the airfoil and extends beyond the airfoil so to overhang it, the resulting mechanical stresses are magnified and concentrated in the supporting fillet, which makes the size, shape, and overall mass of the tip shroud a critical design consideration. Tip shrouds, though, require a certain size and coverage to perform adequately as a seal. In general, such competing mechanical and aerodynamic considerations, make the design of tip shrouds a challenging problem,
One significant component of this design is the profile of the tip shroud. As will be seen, tip shroud profile is the size of the tip shroud—i.e., the extent to which it extends beyond and overhangs the airfoil—as well as the shape of the tip shroud—i.e., the nature of the contoured edges that define the shape of the tip shroud. To be successful, a tip shroud profile must offer size and coverage so to promote sealing functionality, while maintaining an overall mass that can be mechanically supported by a fillet that does not overly compromise aerodynamic performance. Further, tip shroud profiles having even small mass imbalances can result in a significant difference between the stresses within the pressure and suction sides of the fillet region, which can negatively impact the creep life of the blade. Tip shroud profiles, thus, must be precisely tuned to offer enough coverage for achieving a high-level of sealing performance, while removing as much tip shroud mass as possible—and finely balancing the remainder—so that the tip shroud can be adequately supported by an aerodynamic fillet for a long creep life.